Organic material layer adhesion, in the form of photoresist adhesion, to substrates having a layer of low surface energy material such as Teflon AF® present on the surface, and the adhesion of low surface energy materials to a substrate surface, is very poor using current methodology. The result is a reduction in the quality of photolithography processing, and the inability to incorporate low surface energy materials into the layers of a multi-layer device. There have been several attempts to improve the adhesion of organic materials, such as photoresists, to the surface of various substrates having as a top surface a low surface energy material present. Absent any pretreatments, organic photoresist materials will not wet low surface energy surfaces, and so do not coat these surfaces in a way that facilitates patterning. While many surface pretreatment options have been utilized, these conventional procedures have failed to demonstrate the adhesive durability required to complete all necessary processing steps. Some of these procedures produce an effect which is very transitory in nature, while with others, photoresist layers have been observed to peel away from wafer surfaces during development steps or during immersion in cleaning solutions such as an ammonium hydroxide (NH4OH) solution (10% in water). This NH4OH solution is commonly used to clean the wafer surfaces prior to subsequent processing steps such as etches or depositions.
Several attempts have been made recently with respect to pretreatment options to modify the surfaces in an effort to promote resist adhesion. These options have included, dehydration bakes, application of both i-line and DUV anti-reflective coatings used as thin film interlayers, standard HMDS vapor priming, and the application of several silane based organic coupling agents. However, none of these processes has improved adhesion adequately.
The current industry standard process used as a means to prepare silicon wafers for resist coating is to vapor prime wafer surfaces with hexamethyldisilizane (HMDS). However, HMDS is only chemically compatible with silicon and its oxides and does not react in the same manner with most other materials. On a silicon surface, HMDS applies, from the vapor phase, an organic monolayer which is repellant to water or other aqueous solutions such as developers or NH4OH. The water repellant nature of the film at the substrate/resist interface maintains enough surface energy to permit resist to stick and form a film, but prevents the lifting of resist films during subsequent aqueous processing such as developing or cleaning. It is known that the contact angle of water on a surface is a good measure of the surface energy and water repellency of that surface. The contact angle of a water droplet on a properly HMDS-primed silicon surface typically measures between 65–72°. It has additionally been found that traditional vapor priming lasts only three days until the wafers must be primed again. In addition, during the vapor priming process, wafers are typically brought to a temperature of 150° C. for a period exceeding 30 minutes. This is objectionable for certain temperature sensitive applications, and as previously stated, vapor priming with HMDS has no effect on most low surface energy materials such as Teflon or other fluoropolymers.
As previously stated, other methods exist to promote adhesion of organic materials to surfaces of the wafer, more specifically surfaces of the low surface energy material. One such method, often used to modify surfaces which are inert to vapor priming, is to use a chemical vapor deposition (CVD) process to apply a thin (<500 A) layer of a second material such as silicon nitride (SiN) or silicon oxide (SiO) to the surface. The deposition of this material when coupled with traditional HMDS vapor priming, provides for excellent adhesion of the resist layer to the wafer surface. However, such coatings must be later removed which can present additional problems. For example, it has been found that removal of the SiN material, generally through dry etching techniques, is very aggressive and can lead to damage of a fragile wafer epi layer.
Still other methods exist to promote adhesion of photoresist to wafers, such as using oxygen plasma to roughen and add oxygen to the surface prior to coating the surface with resist. This process temporarily raises surface energy, but results in only a transient effect since low surface energy functional groups in the molecule re-migrate to the surface restoring its original low level of energy. In addition, the surface roughness remains which may not be desirable. In the instance where amorphous Teflon AF® is used, the oxygen plasma roughens the Teflon AF® surface, and promotes increased adhesion, but allows for resist solvents to attack the Teflon AF®. It has additionally, been proposed to utilize surfactants mixed with the photoresist materials to aid in surface wetting. The process is complicated and requires double resist coats since wetting by the first coating usually remains incomplete. Typically, 10–15% of the surfactant is needed relative to the resist, yet results in only an 80% coverage with a first coat.
Lastly, other materials have been used as interfacial adhesion promoters. Aluminum has been used, yet aluminum etches in the resist developer, thereby limiting resolution.
Accordingly, it is an object of the present invention to provide for a device, such as a semiconductor device, a photonic device, a microfluidic device, an acoustic wave device, an imprint template, or the like that includes an interfacial material that promotes enhanced adhesion of a photoresist to a low surface energy material or enhanced adhesion of a low surface energy material to a substrate.
It is a further object of the present invention to provide for a device that includes an interfacial material that promotes enhanced adhesion in which subsequent removal of the resist and interfacial layer does not damage the underlying material surface.
It is a further object of the present invention to provide for a device that includes an interfacial material that promotes enhanced adhesion and allows use of the resist layer in a conventional way coupled with a conventional etch process to pattern the low surface energy layer.
It is yet another object of the present invention to provide for a method of fabricating a device including the steps of providing for an interfacial material that promotes enhanced adhesion of a photoresist to a low surface energy material or enhanced adhesion of a low surface energy material to a substrate.